1. Field of Invention
The present invention relates generally to a wind energy conversion device, more particularly, to the design and manufacturing of a jet assisted counter rotating wind turbine.
2. Description of Prior Art
Wind turbines of various designs are in use to generate electrical energy. A wind turbine generally comprises of a rotor having plurality of airfoil shaped blades, an alternator, and a supporting structure. Heretofore, wind turbine manufacturers employ a single rotor system that comprises of two or more said blades. An alternator consists of a rotor, generally having permanent magnets and an armature comprising of plurality of wound coils. Said armature is fixed to said structure, while the magnetic rotor is connected to said turbine rotor. The relative speed in the air gap between the outer surface of said magnetic rotor and the inner surface of said armature is directly proportional to said turbine rotor speed. When the wind speed is less than the cut-in speed, for example 12 miles per hour, said wind turbine system ceases to produce useful electrical energy. Another serious drawback of such conventional wind turbines is that they require large diameter rotors to extract energy from the wind. Large blades require thicker gage materials to minimize failure due to vibration and dynamic loads in gusty wind environment. In spite of careful design and regular inspections many wind turbines in the wind farms suffer structural failures and become inoperative. Thus, the wind turbines of prior art are, mechanically inefficient, prone to catastrophic failures, and not competitive in price per kilowatt-hour.
To alleviate these problems, jet assisted counter rotating wind turbine of the present invention is proposed. The new design has the advantage of substantially increased energy conversion efficiency, reduced cost of ownership, reduced operating cost and increased structural durability. The prior art abounds with examples of single rotor turbine systems. A number of patents disclosing typical inventions pertinent to the present invention will now be presented.
U.S. Pat. No. 4,976,587 to J. Ford Johnston et al (Dec. 11, 1990) discloses a method for manufacturing composite blades having highly improved aerodynamic efficiency. They used the NASA airfoil section LS(1)-04XX having 29 per cent thickness at 3/10 radius and 18 per cent at the blade tip. The airfoil section comprises of two spars, which terminate into a circular section at the hub. The claim primarily relates to the manufacturing aspect of composite blades. However, similar to any other conventional wind turbines, their design uses a single rotor having three aerodynamically efficient blades. However, this design does not extract major portion of the available wind energy.
U.S. Pat. No. 5,419,683 to Steven J. Peace (May 30, 1995) discloses a method of installing plurality of wind turbines on chimney, tower or the like. Two rotors having their horizontal axes are mounted back to back on a ring that turns about the chimney. The primary idea of this invention is to utilize existing structures to mount plurality of wind turbines and to eliminate the need for wind farms. The major drawback is that the unsteady vorticities shed from the chimney impinge up on the leeward rotor and excite the blades to vibrate violently to destruction. Hence, this concept is not practical, and moreover it is aerodynamically inefficient.
U.S. Pat. No. 4,648,801 to Robert R. Wilson (Mar. 10, 1987) discloses a method of compressing air by means of a wind turbine. The air is drawn from the low energy region of the downwind stream. The compressed air is connected to the intake of a prime mover (such as a diesel engine, a gasoline engine, or a gas turbine) to boost its output power. This prime mover drives an alternator. Although the integration of the air compressor is a novel idea, the overall efficiency decreases due to mechanical loses that arise from additional units such as the prime mover and the alternator.
U.S. Pat. No. 5,456,579 to Timothy G. Olson (Oct. 10, 1995) discloses a wind turbine blade with a governor to maintain optimum rotational speed and more particularly pertains to a governor that positions an aileron for varying wind speed. The governor consists of a lead weight positioned at the wing tip and connected to a mechanism that deploys said aileron to achieve the maximum lift to drag ratio at all wind speeds. This is another novel idea, but the operational mechanisms are not robust and are prone to malfunction due to bending and twisting of the blade in gusty wind environment.
It was with the knowledge of the foregoing state of the technology that the present invention has been conceived and is now reduced to practice.